Apparatus for making circular sound tracks



ug. 4, 1959 Y. LEMOINE 2,897,710

APPARATUS FOR MAKING CIRCULAR SOUND TRACKS Filed Sept. 9, 1955 INVEN Yy Lame/me United States Patent APPARATUS FOR MAKING CIRCULAR SOUND TRACKS Yves Lemoine, Marigny, France Application September 9, 1955, Serial No. 533,454

3 Claims. (Cl. 84-128) This invention relates to a method of making circular sound tracks which is particularly suitable for producing modulating discs for photo-electric musical instruments.

It is known that such musical instruments comprise a light source emitting a parallel light beam in the path of which shutters can be moved to control the passage of one or several spots falling on one or several tracks of a modulating disc and thence onto a photo-electric cell.

It will be evident that for good sound quality each track must be as regular as possible, that is to say it must consist of a certain number of signals of predetermined form distributed regularly around a circumference.

In the production of these tracks, expedients have been tried to obtain regularity. The method basically safest for a theoretically reliable and inexpensive reproduction of the discs consists in photographing the tracks on a sensitive plate. In practice the method meets with grave difficulties owing to the relatively large size of the surface of the disc. The method which has been the mostsatisfactory in principle up to now has been to photograph at regular intervals a light source of determined shape mounted on the end of a clock hand so as to obtain a series of identical signals at regular intervals on the same plate. This method is evidently very slow.

The present invention provides a much more rapid and certain method of recording tracks of this kind, which depends on the use of stroboscopy.

According to the invention, each track circuit of a photographic image of a light source which is modulated at a certain frequency while the disc and light source are relatively rotated about a common axis which does not pass through the light source, the speed of the relative rotation being a sub multiple of the modulation frequency of the light source, so that the density of the optical image of the tube on the disc is caused to vary by a stroboscopic effect with a frequency equal to the frequency of the musical rate to be reproduced, that is to the ratio of the frequencies of excitation of the light source and rotation of the disc relatively to the source.

The change from one note to another is effected by changing the track. To pass from one track to another in accordance with the invention therefore, it is sufficient to alter the distance of the light source from the axis of rotation at the same time altering the excitation frequency of the light source so as to alter the number of signals in the track correspondingly (it being understood that signal means a series of separate points as well as a continuous track).

In the same way a change of tone is obtained by changing the shape of the image of the light source by means of a diaphragm arranged in the optical system that forms the image of the light source on the disc, in the case in which the track constitutes a series of separate images.

ice" ables the corresponding note to be heard and verified by the production of a stationary stroboscopic image of the track.

According to an important modification it is possible not only to use a track composed of separate images, but to use as the track any continuous band of variable optical density. This could be for example a band of constant width having an optical density which varies from one cross section to another but remains constant throughout any given cross section. Or it could be composed of a clear part separated from a dark part by a wavy line, the mean density of the clear and dark parts in any transverse section being equal to the above-mentioned constant density throughout a given section of a band of the type previously referred to. (Bands of the last-mentioned type are also known as variable surface tracks as compared with variable density tracks properly so called.)

In both cases, the variation in the density of the track corresponds to the modulation of the illumination of a gas-tube or even of an incandescent lamp by means of a stroboscopic system as described above.

Another modification consists in the use of a musical note having a single very stable frequency for producing a number of tracks. The single note is recorded on a magneto tape or strip and then the strip is scanned at different speeds so as to obtain notes of different frequencies. Control of the scanning speed is obtained by means of a synchronous motor fed by an oscillator of variable frequency which is itself very stable.

The modulation voltage obtained as the output of the magnetic recorder-reproducer, after suitable amplification, is applied to a gas-tube (or incandescent lamp) the image of the light from which, thus modulated, is applied to the photographic disc previously described.

This process could be extended to the reproduction of any tone, starting from the registration of the abovementioned tone on a magnetic strip.

It is even possible to group on the same strip not only several tones of the same pitch but also several notes of different frequencies each having several tones, the track thus formed corresponding in the photo-electric musical instrument to the emission of the corresponding chord.

It will thus be seen that this method has a practically unlimited field of application, the discs being equally useful in photo-electric organs, or considered as novel musical instruments themselves. 7

Finally, instead of a disc, any solid of revolution, for example a cylinder or cone, can be used as the support for the tracks, and could thus carry a greater number of tracks than a disc.

The invention will be better understood from the following description with reference to the accompanying drawing which shows a diagrammatic section of a simple construction for carrying out the method of the invention.

This drawing shows a circular photographic plate 2 and a circular plate 3 mounted in a fixed frame 1 the plate 3 being coaxial with the plate 2 and carrying a lightsource 4. The light source 4 is fixed to the plate 3 by any convenient means which will enable its distance from the axis of rotation to be adjusted. An image of this source is formed by an optical system 5 having a diaphragm 6 which determines the form of the signal 7 on the plate 2.

The plate 3 is driven through a suitable transmission such as a belt 8 by a synchronous motor 9. The lamp 4 is connected through a rotatable contact device, not shown, to an oscillatory circuit 10 which also feeds an amplifier 11 and loud-speaker 12 for verifying the frequency.

As previously explained, the oscillation frequency of the circuit 10, checked by comparing the note given by the loud-speaker 12 with a tuned musical instrument,.

determines the number of signals 7 on the plate as a function of the speed of rotation of the plate 3. On the one hand, the note is altered by adjusting the distance of the lamp 4 from the axis and the oscillation frequency of 10, and on the other hand, the tone is altered by means of the diaphragm 6.

For example, to register a track containing 220 signals, the oscillator 10 is adjusted to 1100 cycles per second. The plate 3 rotates at the rate of revolutions per second. The number of signals on the plate 2 is thus equal to 1100:5=220. For a clear track it is naturally necessary that the 220 signals should be produced at fixed points, that is that the track should be truly immobile. The immobility can easily be checked with the naked eye.

The construction in which the light source rotates and the photographic plate is fixed could evidently be replaced by an inverse construction in which only the photographic plate rotates.

Instead of the gas-tube any other light source that can be excited with a controllable frequency may be used.

What I claim is:

1. A sound recording system of the type producing records of sounds of a predetermined frequency translatable into musical tones on a circular track of a light sensitive disk, comprising a light source the light emission of which is directed towards the light sensitive disk and is controlled by electric currents, means producing said currents, including means producing periodic variations of said light emission controlling currents at apredetermined frequency, thus producing a periodic variation of the light emitted towards the light sensitive disk at the said predetermined frequency, and means producing a relative rotation of light source and light sensitive disk around an axis which is located at a distance from the light source, at a rotational speed measured in c.p.s. which is an integral fraction of the frequency of the light emission controlling currents measured in c.p.s., thus producing a re-entrant sound track with a number of recorded light signals which is equal to the quotient of predetermined frequency and rotational speed.

2. A sound recording system as claimed in claim 1 wherein the variations of the light emission controlling currents are produced by a magnetic tape moving at a constant predetermined speed during production of one sound track and wherein means are provided for varying the speed of the magnetic tape between successive operations, thus producing light emission controlling currents of different frequency in successive operations, resulting in a number of light signals recorded on the light sensitive disk corresponding to tones of different frequency in successive operations.

3. A sound recording system as claimed in claim 2 wherein the distance of the light source from the axis around which relative rotational movement of light source and light sensitive disk occurs is adjustable, to

place re-entrant sound tracks containing the record of sounds of dilferent pitch in proximity to each other.

References Cited in the file of this patent UNITED STATES PATENTS 1,967,238 Goldthwaite July 24, 1934 1,967,239 Hardy July 24, 1934 2,563,647 Hammond Aug. 7, 1951 2,585,291 Wittel Feb. 12, 1952 

